Inks having low rub-off properties are known in the prior art. Such inks typically contain waxes of various types and the resultant inks will exhibit improved mar-resistance, slip and water repellency properties. Wax of a controlled fine particle size can be mixed or ground into the batch along with pigments or may be introduced during the final blending operations. Alternatively, the wax may be compounded into a "wax media" by dispersing or melting the wax into the varnishes and/or solvents and adding these to the ink.
It is generally well-known that the non-rub qualities imparted by an individual wax are a function of both the particle size and the hardness as well as the melting temperature of any particular wax. However, addition of waxes to inks in order to solve the rub-off problem introduces other problems. Firstly, on a scale of 100 representing no rub-off, waxes added to inks will result in reduction in rub-off to a level of only about 60. Secondly, with the heat and movement imparted by the friction of constant rubbing under pressure, particles of the ink film can ball up and mark unprinted areas. Additionally, the more waxes that are added to improve rub resistance, the more problems are introduced in respect to gloss and hardness characteristics. Addition of waxes to inks almost invariably decreases their gloss. Accordingly, a compromise must be achieved between the desired level of non-rub properties and gloss. Finally, there is the factor of increased cost associated with the ink containing relatively expensive waxes such as microcrystalline waxes and polytetrafluoroethylene waxes. In the case of news inks, cost is an extremely important factor and, therefore, at the present time news inks do not ordinarily contain any waxes; furthermore, waxes provide only minimal reduction of rub-off in news ink formulations.
Synthetic waxes such as polyethylene waxes and polytetrafluoroethylene waxes are now the most popular waxes used in the ink industry. Such waxes are usually added in the form of "non-rub" or "slip" media which are fine dispersions of the wax in the solvents, oils and resins, etc., of the particular type of ink formulation in which it is to be incorporated. Waxes prepared from polytetrafluoroethylene powders are suitable for all types of printing inks, but are especially ideal for heatset inks, where the temperature of the drying apparatus does not cause them to soften or melt. Polytetrafluoroethylene-based waxes can also be stirred into finished inks to improve their rub and scuff resistance. Nevertheless, the relative cost of a polytetrafluoroethylene wax is prohibitively high for many applications, e.g. news inks.